Associations of physical activity with body weight and fat in men and women

OBJECTIVE: Increasing physical activity is strongly advocated as a key public health strategy for weight gain prevention. We investigated associations of leisure-time physical activity (LTPA) and occupational/domestic physical activity with body mass index (BMI) and a skinfold-derived index of body fat (sum of six skinfolds), among normal-weight and overweight men and women.

DESIGN: Analyses of cross-sectional self-report and measured anthropometric data.

SUBJECTS: A total of 1302 men and women, aged 18-78 y, who were part of a randomly selected sample and who agreed to participate in a physical health assessment.

MEASUREMENTS: Self-report measures of physical activity, measured height and weight, and a skinfold-derived index of body fatness.

RESULTS: Higher levels of LTPA were positively associated with the likelihood of being in the normal BMI and lower body fat range for women, but few or no associations were found for men. No associations were found between measures of occupational/domestic activity and BMI or body fat for men or women.

CONCLUSION: By using a skinfold sum as a more direct measure of adiposity, this study extends and confirms the previous research that has shown an association between BMI and LTPA. Our results suggest gender differences in the relationship of leisure-time physical activity with body fatness. These findings, in conjunction with a better understanding of the causes of such differences, will have important public health implications for the development and targeting of weight gain prevention strategies.

Growth of highly versus moderately trained competitive female artistic gymnasts

Purpose: To investigate whether growth was adversely affected in 137 young competitive female artistic gymnasts involved in different training volumes.

Methods: This was a 2-yr prospective cohort study in which height, sitting height, leg length, weight, skinfolds, and pubertal status were measured in competitive advanced (20–27 h·wk-1) and intermediate (7.5–22 h·wk-1) training level female gymnasts every 6–12 months. Biological parameters of the adolescent growth curve were estimated using the Preece–Baines growth model. Growth rates were estimated for both groups from the mixed-longitudinal data.

Results: Estimated ages at peak height velocity (PHV) (13–13.5 yr) and mean PHV (6.2–6.4 cm·yr-1) for the advanced- and intermediate-level gymnasts suggest that these gymnasts were later maturing and experienced a blunting of the growth spurt relative to reference values for U.S. youth. Comparison of growth velocities by pubertal status revealed that height velocity was lower in the advanced- versus the intermediate-level peripubertal gymnasts, which was due to a significant reduction in sitting height velocity (2.3 vs 3.1 cm·yr-1, P. < 0.05). No marked acceleration in height or sitting height velocity was detected in the advanced-level gymnasts from pre- to peripuberty. Inspection of individual growth rates revealed that over 35% of the pre- and peripubertal gymnasts experienced growth faltering (height velocity less than 4.5 cm·yr-1) during follow-up.

Conclusion: Advanced–and intermediate–training level competitive female gymnasts tend to exhibit an adolescent growth spurt that is similar in timing and tempo to short, normal, slowly maturing girls, but the high frequency of growth faltering suggests that training may alter the tempo of growth and maturation in some, but not all, female gymnasts.

Effect of Jersey type on thermoregulatory responses during exercise in a warm humid environment

The thermoregulatory responses of subjects wearing two different forms of rugby league jersey, one with plastic sponsorship recognition and numbering (trial Gl) and one without (trial G2), and a lightweight alternative (trial G3), were compared with a trial without any form of upper body garment (trial GO). Ten male volunteers, mean age 20.9 (±2.3) years, height 179.8 (±4.7) cm, weight 80.2 (±8.9) kg, and body surface area 1.99 (±0.13) m2, participated in this study. Subjects had a mean maximal oxygen uptake capacity of 56.0 (±6.3) ml.kg.min-1 and a sum of 8 skinfolds of 80.6 (±23.8) mm. Subjects were exercised at approximately 50% of maximal oxygen uptake in a warm humid environment for 50 minutes. Mean ambient temperature was 27.6°C (±0.32) with a relative humidity of 64.7% (±1.44). Measurements of core and skin (7 sites) temperature, heart rate, oxygen uptake, plasma volume, peak lactate concentration, and pre- and post-trial body weight, hematocrit and garment weight were recorded. The statistical results showed that all subjects experienced significant (p ≤.0001) decreases in body weight representing a percentage decrease ranging from 1.2-1.3%. No significant difference was found between trials with respect to body weight change. No significant effect of garment type was found on pre- and post-trial hematocrit, plasma volume changes or peak blood lactic acid concentration. However, mean peak lactate was highest for trial Gl (5.6 mmol.L-1 ±2.2) and lowest for trial G3 (4.6 mmol.L-1 ±1.27). Post-trial core temperature was significantly (p≤ .0001) higher than the resting value; no significant difference was found between trials. The mean absolute increase for all experimental trials was 0.9°C. A significant (p≤.005) difference between mean total (7 sites) skin temperature was found with a post-hoc test revealing that trials Gl and G2 were significantly higher than trial GO; no significant difference was found when comparing trial G3 with trial GO or when comparing the garments between each other. Mean skin temperature under the garment (4 sites) was found to be significantly (p≤.05) higher for all trials involving a garment when compared with mean skin temperature outside (3 sites) the garment; no significant difference was found between trials. Mean oxygen uptake was significantly different between trials (p≤.005), with trial Gl and G3 found to be significantly lower than trial GO; no difference was found when comparing the garments with each other. Post-trial garment weights were significantly (p≤.001) heavier than pre-trial and were significantly (p≤.0001) different when compared with each other. There was no significant effect on heart rate, haematocrit, plasma volume changes, peak blood lactic acid concentration, or core temperature due to garment type. However, differences in skin temperature suggest that the garment used in trial G3 may have a benefit. Further research should consider the impact of increased exercise intensity and/or environmental temperature and humidity on the measured parameters while wearing the garments described in this study.

Maternal 25-hydroxyvitamin D concentration and offspring birth size : effect modification by infant VDR genotype

Background/Objectives: We tested the hypothesis that the relationship between maternal 25-hydroxyvitamin D (25-(OH)D) and offspring birth size differs according to offspring vitamin D receptor (VDR) genotype (Apa1, Bsm1, Fok1 or Taq1).

Subjects/Methods: Mothers of 354 singleton babies had serum 25-(OH)D concentration measured at 28–30 weeks of gestation and consented to measurement of their babies soon after birth. DNA was extracted from the babies’ Guthrie cards.

Results: There was evidence of effect modification by infant FokI genotype. Babies of deficient mothers had lower birth weight with FF or Ff, but not ff genotype (P-value for interaction after adjustment for potential confounding factors=0.02), but thicker subscapular and suprailiac skinfolds with ff, but not FF or Ff genotype (P=0.008 and 0.02, respectively). Sample size was insufficient to investigate effect modification by the other VDR polymorphisms.

Conclusions: These preliminary findings suggest that studies of maternal vitamin D status and birth size may need to take VDR genotype into account.

Body fat estimated from anthropometric and electrical impedance measurements

Estimates of body fat based on anthropometric measurements were compared in two groups of females, one from the local community and the other from the 1984 Australian Olympic Team. Estimates of body fat based on electrical impedance measurements were also made for the community group. For estimates of total body fat based on skinfold measurements, a significant difference of approximately 1 kg fat/m2 was observed between athletes and non-athletes. In the group of non-athletes estimates of fat based on skinfold measurements were significantly higher than those based on body mass index, with estimates from electrical impedance falling between. Electrical impedance measurements may provide a means of estimating body fat which takes into account differences in fat distribution and in the ratio of fat to fat-free tissue and may thus overcome the problems associated with estimates based on measurements of subcutaneous fat (skinfolds) or body size which do not allow for these differences.

The influence of body build on estimates of body composition from anthropometric measurements in premenopausal women

Objective: To assess the influence of body build on the bias and limits of agreement for estimates of body fat obtained from anthropometric prediction equations when compared with the same data obtained by dual energy X-ray absorptiometry (DEXA).

Survey design and subjects: Ninety-one premenopausal women, aged between 20 and 54 years, were chosen to represent a range of skeletal body build (relative silting height 0.50-0.56) and body fatness [body mass index (BMI) 18-34 kg/m²]. Measurements of weight, sitting height, stature, skinfold thickness, waist, umbilical and hip circumference and total body resistance and reactance were made on all subjects by standard techniques after an overnight fast. A DEXA measurement of total body fat, fat-free soft tissue and total body bone mineral mass was also obtained within 2 weeks of the anthropometric assessment.

Results: At the group level the mean difference (bias) between DEXA and the anthropometric estimates of body fat was similar for all three anthropometric estimates ranging from 2.7 kg with impedance to 1.8 kg with skinfold thickness. The 95% limits of agreement were also similar, ranging from ±5.3 kg with body mass index to ±4.1 kg with impedance. Umbilical circumference, BMI and the amount of bone mineral expressed as a proportion of the fat-free soft-tissue mass were all significantly (P < 0.01) correlated with the level of bias between DEXA and the anthropometric estimates of body fat. This was not the case for relative sitting height or measures of body fat distribution. Regression equations which included BMI or umbilical circumference in combination with the predicted estimates of body fat essentially eliminated the association between the level of bias in predicted body fat and the level of body fatness. They also reduced the 95% limits of agreement between DEXA and the anthropometric estimates of body fat.

Conclusions: Using DEXA estimates of body fat as the standard of reference our results suggest that the comparability and precision of body fat estimates derived from age- and/or sex-specific anthropometric prediction equations based on skinfolds and BMI, but not impedance, can be improved by adjusting for differences in BMI and umbilical circumference respectively.

Active commuting to school and association with physical activity and adiposity among US youth

Background: Walking or bicycling to school (ie, active commuting) has shown promise for improving physical activity and preventing obesity in youth. Our objectives were to examine, among US youth, whether active commuting was inversely associated with adiposity and positively associated with moderate-to-vigorous physical activity (MVPA). We also examined whether MVPA mediated the relationships between active commuting and adiposity.

Methods: Using data of participants aged 12 to 19 years from the US National Health and Nutrition Examination Survey 2003 to 2004 (n = 789 unweighted), we constructed multiple linear regression models that controlled for dietary energy intake and sociodemographics. The main exposure variable was active commuting. The outcomes were BMI z-score, waist circumference, skinfolds and objectively measured MVPA. The product-of-coefficients method was used to test for mediation.

Results: Active commuting was inversely associated with BMI z-score (β = –0.07, P = .046) and skinfolds (β = –0.06, P = .029), and positively associated with overall daily (β = 0.12, P = .024) and before- and after-school (β = 0.20, P < .001) MVPA. Greater before- and after-school MVPA explained part of the relationship between active commuting and waist circumference (Sobel z = –1.98, P = .048).

Conclusions: Active commuting was associated with greater MVPA and lower measures of adiposity among US youth. Before- and after-school MVPA mediated the relationships between active commuting and waist circumference.

Olympic weightlifting and plyometric training with children provides similar or greater performance improvements than traditional resistance training

A number of organizations recommend that advanced resistance training (RT) techniques can be implemented with children. The objective of this study was to evaluate the effectiveness of Olympic-style weightlifting (OWL), plyometrics, and traditional RT programs with children. Sixty-three children (10-12 years) were randomly allocated to a 12-week control OWL, plyometric, or traditional RT program. Pre- and post-training tests included body mass index (BMI), sum of skinfolds, countermovement jump (CMJ), horizontal jump, balance, 5- and 20-m sprint times, isokinetic force and power at 60 and 300° · s(-1). Magnitude-based inferences were used to analyze the likelihood of an effect having a standardized (Cohen's) effect size exceeding 0.20. All interventions were generally superior to the control group. Olympic weightlifting was >80% likely to provide substantially better improvements than plyometric training for CMJ, horizontal jump, and 5- and 20-m sprint times, whereas >75% likely to substantially exceed traditional RT for balance and isokinetic power at 300° · s(-1). Plyometric training was >78% likely to elicit substantially better training adaptations than traditional RT for balance, isokinetic force at 60 and 300° · s(-1), isokinetic power at 300° · s(-1), and 5- and 20-m sprints. Traditional RT only exceeded plyometric training for BMI and isokinetic power at 60° · s(-1). Hence, OWL and plyometrics can provide similar or greater performance adaptations for children. It is recommended that any of the 3 training modalities can be implemented under professional supervision with proper training progressions to enhance training adaptations in children.

Characterizing changes in fitness of basketball players within and between seasons

We assessed the magnitude of changes in fitness and anthropometric test scores of well-trained basketball players between phases of a year and over several years. Players were 1011 females and 1087 males in Basketball Australia's State and National junior programs (1862 and 236 players respectively). Players undertook a set of three fitness and three anthropometric tests on 2.6 ± 2.0 (mean ±SD) occasions over 0.8 ± 1.0 y. Mixed modeling was used to estimate mean changes within and between seasons, and to estimate individual variability as the standard deviation of change scores between assessments. Changes were expressed as standardized (Cohen) effect sizes for interpretation of magnitudes (trivial <0.2; small 0.2-0.6, moderate 0.6-1.2). In the first 2 y National and State males showed small longitudinal improvements in body mass, skinfolds, and shuttle-run performance (effect size 0.28 – 0.42). After 2 y National females made small improvements in most tests (0.27 – 0.42), but National males showed a small decline in shuttle-run performance (0.55). Other changes in mean test scores within and between seasons were trivial. Individuals showed small to moderate variability about the mean change between phases (0.23 – 0.87) and between years (0.26 – 1.03), with State-level players having greater variation in all tests (State/National ratio 1.1 – 2.4). Coaches or sport scientists monitoring or modifying fitness of basketball players should recognize there is generally little overall change in mean fitness within and between seasons. They should also take into account the small to moderate changes in individuals.